1. Field of the Invention
This invention relates to a relief valve which operates when an internal pressure is increased to or above a predetermined value, thereby discharging an inner compressed fluid outside.
2. Description of the Related Art
FIG. 8 illustrates one of conventional relief valves of the above-described type, for example. The illustrated relief valve comprises a cylindrical member 1 mounted to a pipe conduit 5 or a vessel, a nozzle 2 provided in the cylindrical member, a movable valve element 3 pressed by a compression coil spring 4 against a discharge port of the nozzle. When pressure in the pipe conduit 5 has been increased to or above a predetermined value, the movable valve element 3 is departed away from the discharge port against the spring force of the compression coil spring 4, whereupon the an inner fluid is discharged outside. JP-A-2001-271950 discloses a relief valve of the type described above.
In the above-described relief valve, the movable valve element 3 is moved in a direction of flow of the fluid discharged outside (for example, in the direction of arrow A in FIG. 8). Accordingly, for example, the movable valve element 3 is moved in the direction perpendicular to the direction in which the compressed air in the pipe conduit 5 flows, that is, in an axial direction with respect to the pipe conduit 5 as shown by arrow B in FIG. 8. Thus, the movable valve element 3 protrudes sidewise from the pipe conduit 5. This structure requires a larger space in the direction of flow of compressed air.
Therefore, an object of the present invention is to provide a relief valve which has a compact structure.
The present invention provides a relief valve which operates when an internal pressure is increased to or above a predetermined value, thereby discharging an inner compressed fluid outside.
The relief valve comprises an outer stem formed into a cylindrical shape and having both open ends, the outer stem including a larger diameter fitting section and a smaller diameter fitting section both having inner diameters differing from each other and aligned axially. A movable valve element is formed into a cylindrical shape and having both open ends. The valve element is fitted in the larger and smaller diameter fitting sections so as to be moved between an opening position at the smaller diameter fitting section side and a closing position at the large diameter fitting section side. A communication space is defined so as to extend through the outer stem and the movable valve element so that a compressed fluid flows therethrough from one end of the outer stem to the other end of the outer stem. A first normally closed seal is provided between the valve element and the smaller diameter fitting section for closing a part of a circumferential gap defined between the valve element and the outer stem. The part of the circumferential gap extends from the smaller diameter fitting section side to the communication space. A second seal is provided between the valve element and the larger diameter fitting section for closing a part of the circumferential gap extending from the larger diameter fitting section side to the communication space when the movable valve element has been moved to the closing position, the second seal opening said part of the circumferential gap when the movable valve element has been moved to the opening position. A relief hole is formed in the outer stem so that the circumferential gap normally communicates with an atmosphere outside the outer stem irrespective of a position of the valve element. A holder is provided for holding the valve element at the closing position by means of a holding force. A pressure wall protrudes from the valve element inside the larger diameter fitting section to move the valve element to the opening position side when a pressure in the communication space is increased to or above a predetermined value while the valve element is at the closing position.
The compressed fluid flows through the communication space defined so as to extend through the cylindrical stem and valve element. The valve element is moved in a flowing direction of the fluid or axially with respect to the stem. When the pressure in the communication space is smaller than the predetermined value, the valve element is held at the closing position such that a passage between the stem, valve element and the relief hole is closed. When the pressure in the communication space is increased to or above the predetermined value, the internal pressure applied to the pressure wall moves the valve element to the opening position hole such that the compressed fluid is discharged from the relief hole outside the stem. Consequently, the fluid pressure in the communication space is controlled so as not to exceed the predetermined value. Thus, since the valve element is moved axially with respect to the stem, the valve element is prevented from protruding sidewise from the pipe conduit, whereupon the structure of the relief valve can be compacted.